Phase shifting circuit



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PHASE SHIFTING CIRCUIT Filed may 9, 1944 v ,20 l ,4 [/7 Wig; ig; l @#2 EN/5 @E img?, 5MM

:Patented Novi r1946 rmsnsmr'rmo cmcnrr Heath It. Guptill, Washington, General Electric Company,

New York D. C., assignor to a corporation of Application May 9, 1944, Serial No. 534,769 3 (01.'172-238) trical degrees in order to obtain optimum operationoij such an apparatus.

It is an'obiect of my invention to provide a new and improved electric phase shifting circuit.

It is a further` object off-my invention to provide a new and improved electric kphase shifting circuit of the static impedance type in which the output voltage may be varied through 360 electrical degrees relative to the input voltage.

It is another object of-my invention to provide an improved electric phase shifting circuit which is simple in assembly and operation and which requires only variable v phase variation of 360 electrical degrees.

For a better understanding of my invention, reference may be had to the following descrip.- tion taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims. Flg.x1 diagrammatically illusstrates an embodiment illustrates a variable f resistance arrangement which may be employed in the circuit of Fig. l,

Referring to Fig. 1, there is shown a phase shift circuit `of the static impedance type which includes a winding I across which is impressed an alternating voltage. 'I'he winding I may be the a transformer having a primary winding 2 connected to a source of alter- The winding I is provided with a pair of output terminals 4 and 5 and an electrically intermediate terminal 6 which is connected to ground so that the alternating potentials appearing across the terminals 4 and 5 are balanced with respect to ground.

Output terminal 4 of winding I is connected to the common point 1 of a pair of reactance elements comprising a iixed capacitance 8 and a fixed inductance 9 connected in'series at their opposite ends through a resistor I0. The resistor I is provided with a variable point or contact II which Is directly connected to an output terminal I2 of the phase shifting circuit. The other output terminal I3 of the phase shifting circuit is resistances to obtain a Vmediate connection 6 of winding I.

the resistance oi' contact I5 produces o, shift in of my invention and Fig. 2

connected directly to ground so that it is maintained at the potential of the electrically inter- The variable contact II on resistor I0 is likewise connected to the through a variable resistance I4. The resistance I 4 is shown as havinga contact I5 adjustable in position along the length ci the resistance to vary connected between contact II and terminal In the operation of the phase shifting circuit, the two variable contacts I5 and," are moved in a certain sequence in order to obtain a phase shift which progresses continuously in one direction without discontinuitiesv or reversals. This sequence consists in starting the contact II at the upper terminal of resistor I0 and contact I 5 at the lower 'terminal of resistance I4 so that the resistance between output terminal I2 and terminal 5 has a value of zero. The contact I5 is moved along resistance I4, changing this resistance to a maximum value. This movement phase in the voltage of output terminals I2, I3 with respect to the voltage across input terminals 4, 5 of slightly less than degrees. Thereafter, contact II is moved along resistor terminal to ditional` phase shift of between ten and twenty degrees.

so the sequence may be repeated. This particular order of adjusting the variable elements in the phase-shifting circuit produces a phase shift which progresses always in the same direction. If the sequence is reversed,

. the phase shift is continuous in the opposite direction. Any other desired sequence of operaemployed but the advantage of essentially constant-amplitude and essentially uniform phase shift is sacrificed.

In Fig. 2 there is shown a potentiometer arrangement which is particularly adapted for use in the phase shifting circuit of Fig. -l. 'In this ligure, elements corresponding to those in the circuit of Fig. l are designated by correspending reference numerals. The two resistance units I8. Il each have a value which is opposite terminal Iiof winding I.

I 0 from its upper its lower terminal to produce an adtwice the value of the corresponding -resistor I4 shown in the circuit of'Fig. l. The points Y I8-2I correspond to the points indicated by like reference numerals 'in Fig. 1. The resistance units I 8, I1 are connected in parallel between the equipotential points I8, I9 by means of conductor 22 of low resistance value to form the inner resistance element of a potentiometer. 'Ihe two ends l connected thereto similar conductors 23, -2I to form the outer resistance element of a double potentiometer arrangement. vAt a point opposite the point I8 on the inner potentiometer` element, the conductors overlapping contact strips 25. 28, which form a cross-over element in the outer potentiometer. The variable contact points II, I5 are mechanically linked for uni-control operation. The resistances I8, I1 and III are so arranged in the potentiometer that, as the contacts II, IB are moved clockwise from the terminals I8, 25, first, the eective resistance value of resistors I6, Il is varied-from a value of zero with respect to point I8 to a maximum value at point I8. Throughout this motion, the value of resistance I is unchanged, the contact I5 remaining electrically at the potential of point 2t. Additional movement varies the contact point il from the capacitance end of resistor I@ to the inductance end. i. e., from terminal 20 to terminal 2i. .Ad-

`ditional clockwise movement of contacts II, I reduces the effective resistance value of resistors I1, It between points i8, I9 from a maximum value to zero value and completes a phase shift of 360 electrical degrees. Thereafter, the contact I i moves across the contact strips 25, 2liv changing the contact Ii from the inductance end of the resistor It to its capacitance end, and preparing the circuit for another phase shift of 360 electrical degrees.

In the phase shift circuit described, in order to obtain a shift in phase which varies substantially uniformly with angular movement of the contacts Il, I5, resistors I6, I'I preferably may be logarithmic in character, while resistor I0 preferably has a linear resistance characteristic. The relation of the resistance between point I8 20, 2I of resistance unit I0 have" 23, 24 are terminated in' and the slider l5 to the angle of electrical phase shift is represented by the following equation:

tang-gl)- where R=resistance between point I8 and slider I5 X--reactance of element 8 or 9- a=phase shift angle for zero angle a, then increases at a constantly increasing rate until it reaches an innite value a,41 1,4as

at an angle of or '1r radians, for X. A potentiometer having an approximately logarithmic taper approaches this function. l

The exact phase shift obtained by variation A of either of the contacts I I, I5 depends, of course,

upon the particular values of resistances used for elements I0, I6, II and the reactances of elements 8; 8. Likewise, the change in amplitude of the output voltage depends upon the relative values of these resistances and their magnitudes, as compared with the impedances of the reactance elements of the circuit. In general, a substantially uniform shift in phase may be obtained with a variation in amplitude of less than-50 per cent.

While I have shown a particular embodiment of my invention, it will, of course, be understood that I do not wish to be hunted thereto since various modications may be made, and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

-1. In combination, a source of alternating voltage having a pair of output terminals balanced with respect to ground, a load connected between ground and one of said terminals through a variable resistance, a pair of vreactances connected in seriesf through a resistor, said reactances having a common point connected to the other of said terminals, and means connecting said load to a variable point of said resistor.

2. In combination, an alternating current circuit, apparatus for producing an alternating voltage `variable in phase through 360 degrees relative tothe voltage of said circuit comprising a reactance element in said circuit having a pair of terminals and an electrically intermediate connection, a capacitance and an inductance each having one terminal connected to one of said terminals, a resistance connected between the lopposite terminals of said capacitance and said inductance, an output circuit connected be` tween a.' variable point on said resistance and said intermediate connection, and a variable resistance connected between said point and the other of said pair of terminals.

3. Inrcombination, an alternating current circuit, apparatus for producing an alternating voltage variable in phase relative to the voltage of said alternating current circuit comprising a winding energized from said circuit and having a pair of terminal connections and an electrically intermediate connection, a variable resistance a connected between one of said terminals and an output circuit, a resistance having a variable point and connected between said variable re-v sistance and said other terminal through a pairA 

